It doesn't appear to be accessible.
ShapeGroup properties and methods:Code:
,==,active,addProperty,canAddProperty,canSetEnabled,duplicate,elided,enabled,
isEffect,isMask,isModified,matchName,moveTo,name,numProperties,parentProperty,
property,propertyDepth,propertyGroup,propertyIndex,propertyType,remove,selected
ShapePath properties and methods:Code:
==,active,addKey,canSetEnabled,canSetExpression,canVaryOverTime,dimensionsSeparated,
duplicate,elided,enabled,expression,expressionEnabled,expressionError,getSeparationFollower,
hasMax,hasMin,isEffect,isInterpolationTypeValid,isMask,isModified,isSeparationFollower,
isSeparationLeader,isSpatial,isTimeVarying,keyInInterpolationType,keyInSpatialTangent,
keyInTemporalEase,keyOutInterpolationType,keyOutSpatialTangent,keyOutTemporalEase,
keyRoving,keySelected,keySpatialAutoBezier,keySpatialContinuous,keyTemporalAutoBezier,
keyTemporalContinuous,keyTime,keyValue,matchName,maxValue,minValue,moveTo,name,
nearestKeyIndex,numKeys,parentProperty,propertyDepth,propertyGroup,propertyIndex,
propertyType,propertyValueType,remove,removeKey,selected,selectedKeys,separationDimension,
separationLeader,setInterpolationTypeAtKey,setRovingAtKey,setSelectedAtKey,
setSpatialAutoBezierAtKey,setSpatialContinuousAtKey,setSpatialTangentsAtKey,
setTemporalAutoBezierAtKey,setTemporalContinuousAtKey,setTemporalEaseAtKey,setValue,
setValueAtKey,setValueAtTime,setValuesAtTimes,unitsText,value,valueAtTime
ShapePath.value properties:Code:
closed,inTangents,outTangents,vertices
(Properties and Methods above are from CS5.5)
You might have to create a mask and set it to rotoBezier then copy the path to a shapeLayer with hardcoded inTangents and outTangents. It still won't be set to rotoBezier in the shapeLayer, but the inTangents and outTangents will be correct as long as the vertices don't move. If the vertices move then you'll have to set it to rotoBezier manually before running a script to move the vertices.
(ShapeGroup and ShapePath properties and methods haven't changed in CS6)
ShapePath.value properties from CS6:Code:
closed,featherInterps,featherRadii,featherRelCornerAngles,featherRelSegLocs,featherSegLocs,
featherTensions,featherTypes,inTangents,outTangents,vertices